SYSTEM FOR ANALYSING A LOW PRESSURE GAS BY OPTICAL EMISSION SPECTROSCOPY

摘要

The invention relates to a system for analysing gases (2) under pressure of the order of secondary vacuum. The system includes a gas ionisation device (4) that comprises a cathode (14) having conducting walls (12) defining a cylindrical volume (11) and a disc (15) including at least one central through hole (31), an anode (13) placed substantially at the centre of the hole (31), a plasma source, the plasma being generated in the cylindrical volume by the combined action of an electric field E (17) and a magnetic field B (19) orthogonal to the electric field E (17), a system (5) for collecting the light radiation emitted by the plasma, a cylindrical cavity (23) coaxial to the anode (13) having a conductance lower than that of the cylindrical volume (11) and arranged between the ionisation device (5) and the collector system (5), and an analysis device (6) for the ionised gases including an optical spectrometer (41) for analysing the evolution of the radiating spectrum. Preferably, the end of the cavity (23) opposite the cylindrical volume (11) is closed by a hatch (21) that is transparent to the light radiation emitted by the plasma.